Dortmund are four points off Bayern in the Bundesliga, and they have a chance on Tuesday at home to get to within a point.
And Zorc knows that it is a must win game.
"You don't have to be a prophet to say that if we want to play for the title, we must win this," Zorc told a virtual news conference.
"There are only six matches left after that. It's simple, but it will be difficult to execute.
"We need to believe in ourselves, we need to be confident. We need to cope with periods of Bayern dominance. They will have more of the ball. We must defend really well. We must be aware of our own qualities.
"We can always score goals against them and we can beat them."